1. Field of the Invention
The present invention relates to a magnetic disk apparatus in which two head assemblies are arranged at positions offset from each other. The present invention also relates to a head assembly adapted for use in a magnetic disk apparatus.
2. Description of the Related Art
A magnetic disk apparatus used as a memory in computers includes magnetic disks, access arms, and head assemblies arranged to face the magnetic disks. Each head assembly comprises a magnetic head and a flexible arm (called a flexure) attached to the access arm for supporting the magnetic head. A magnetic head accesses a desired magnetic disk to read data stored in the magnetic disk or to write data to the magnetic disk.
In the conventional magnetic disk apparatus, one access arm is arranged between two adjacent magnetic disks, and two flexible arms are attached to one access arm. Magnetic heads are supported at the free ends of the flexible arms, respectively. One magnetic head faces the upper magnetic disk, and the other magnetic head faces the lower magnetic disk, so that each magnetic head can read or write data to or from the respective magnetic disk.
Such a conventional magnetic disk apparatus, as described above, has two sets of magnetic heads and flexible arms arranged at positions laterally offset from each other. In addition, other magnetic disk apparatus similar to those described above have the lengths of the flexible arms different from each other and change the securing points on the access arm for the flexible arms.
Each magnetic head (or a core slider) has rails for receiving an airflow generated by the rotation of the magnetic disks so that the magnetic head flies above the magnetic disk. The magnetic head also includes a magnetic element with a coil, a pole and a gap for reading or writing magnetic data. Typically, the magnetic head has two parallel rails. In recent magnetic heads, the magnetic element with the coil, the pole and the gap are built into the structure of the magnetic head using a semiconductor fabrication technique.
The magnetic head usually includes two magnetic elements therein such that each magnetic element is arranged adjacent to one of the rails. Two flexible arms supporting respective magnetic heads are attached to the access arm in such a manner that two flexible arms are arranged in an exactly overlapped relationship. In some cases, two flexible arms are arranged at laterally offset positions from each other, as described above. However, in many cases, it is desirable that two flexible arms are attached to the access arm in an exactly overlapped relationship so that the upper and lower magnetic heads on either side of the access arm can access the identical tracks of the respectively facing magnetic disks.
Although the magnetic head includes two magnetic element, only one magnetic element is actually used. Therefore, if a magnetic head having only one magnetic element formed therein can be used, it is possible to reduce the cost of manufacturing the magnetic head. Besides, requests for a core slider having a smaller size are increasing, and it is becoming difficult to manufacture a smaller core slider having two magnetic elements formed therein. In particular, if a core slider is smaller than 1.8.times.1.0.times.0.3 (millimeter), it is difficult to form terminals having low resistances. Therefore, it is desired that a magnetic head having only one magnetic element formed therein be used.
However, when the flexible arms are attached to the access arm, two magnetic heads are arranged in positions rotated by 180 degrees to each other. That is, the upper magnetic head is arranged to face the upper magnetic disk, and the lower magnetic head is arranged to face the lower magnetic disk. Now supposing that a magnetic head, which has only one magnetic element formed therein and in which the magnetic element is arranged adjacent to one of the rails (referred here the right rail here for clarity), is used, and that two sets of magnetic head assemblies are viewed from the upper magnetic disk, the head element in the upper magnetic head is positioned at the right end of the upper magnetic head and the head element in the lower magnetic head is positioned at the left end of the lower magnetic head, so that the head elements of the upper and lower magnetic heads are displaced from each other and cannot access the identical tracks on the respective magnetic disks.
Therefore, if a magnetic head having only one magnetic element formed therein is to be used, it is necessary to prepare two kinds of magnetic heads, i.e., one magnetic head having the magnetic element arranged adjacent to the right rail and the other magnetic head having the magnetic element arranged adjacent to the left rail, and the two magnetic heads are arranged to face the upper and lower magnetic disks so that the position of the gap of the upper magnetic head coincides with the position of the gap of the lower magnetic head. While it is possible to use the magnetic heads in such a manner that the position of the gap of the upper magnetic head is displaced from the position of the gap of the lower magnetic head, it is difficult to decide the positions of the magnetic heads and it may be impossible to read magnetic data when one magnetic head is damaged and replaced by a new one, particularly if the density of the tracks of the magnetic disks increases, or if a variation in the products exists.
Therefore, two kinds of magnetic heads must be prepared if a magnetic head having only one magnetic element formed therein is to be used and the manufacturing cost cannot,be reduced. A further problem arises in that the management of two kinds of magnetic heads is difficult, and the management of the head assemblies including such magnetic heads is also difficult.